The use of mobile devices such as cellular telephones and other devices with cellular data connectivity is proliferating. Almost everyone has some sort of mobile, data-enabled device, and some people have multiple such devices. Users can access different networks using a single mobile device, and can access voice, text, and multimedia data from various network-accessible and Internet-accessible entities. Furthermore, mobile device complexity is increasing, with more and more advanced and power-efficient processors, display interfaces, and applications to provide user experiences like never before. Consequently, people are using their mobile devices more frequently, and have larger bandwidth requirements for data, email, voice, etc. This increased usage puts a tremendous strain on cellular networks that provide wireless communication services.
Mobile devices often offer alternative means for wireless connectivity, in addition to cellular connectivity. For example, mobile devices may provide wireless local-area network (WLAN) connectivity, in which the device uses a dedicate radio transceiver to connect through a wireless network access point (AP) to local-area and wide-area networks, including the Internet. WLAN connectivity can also be used to connect with the core network of a cellular services operator. In particular, WLAN technologies such as Wi-Fi can be used to carry data for voice calls, video calls, and SMS messaging. However, this typically requires that the mobile device maintain a constant connection to a wireless network access point as well as actively maintaining a secure data connection with a cellular network gateway through an untrusted and/or public network such as the Internet.